Illustration 34.4: Prisms and Dispersion

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The index of refraction of a given material depends on the wavelength (or frequency) of the incoming light.  So, when the index of refraction of a material is given, it is really only true for one particular wavelength or color of light. This slight variation in the index of refraction leads to chromatic aberrations in lenses (where the focal point is different for different colors) and it is what allows for the separation of white light into colors using a prism (or drops of water).  Restart. 

1. Change the wavelength of light (in air) and therefore change the color of the light entering the prism.  Notice the angle at which the different colors exit the prism and the different index of refraction associated with each color. 
2. You can also move the incident light source around a bit.  Try moving it.  Can you predict (approximately) the direction of the twice refracted ray exiting the prism?
3. When white light enters the prism, what happens?  This is called dispersion.  Explain why you see a rainbow of colors.

Illustration authored by Morten Brydensholt and Anne J. Cox.
Script authored by Morten Brydensholt.
© 2004 by Prentice-Hall, Inc. A Pearson Company